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This article gives some explanation of what a STEVE is https://www.livescience.com/mysterious-aurora-like-phenomenon-steve-appears-during-strongest-solar-storm-for-more-than-half-a-decade.
My latest post has disappeared again due to over editing!! What a nuisance. What I said was that thanks to Grant I think this white arc was a STEVE. I made the point that the red glow in the east to the right of the arc was mirrored in the west by a similar red glow (an aurora?). Also I have calculated that the arc reached a maximum of 60 degrees altitude due north rather than 70 degrees. Further, I would be interested to know if anyone else has seen the fast moving “curtains” travelling along the arc from east to west. They can be best described as bands which were perpendicular to the direction of the arc.
The display seems to have subsided now (20:00 UT) but I just wanted to jot down what I saw whilst it is fresh in my memory. I am in a semi rural location near the Norfolk Broads. Probably about 18:35 I went outside to look at the sky and there was an arc of milky light running almost due east to due west which I thought at first was cloud. I went to grab my camera and the first image I took was at about 18:42. This showed it was definitely an aurora. The arc ran through Perseus in the east, then probably up to 70 degrees above the northern horizon then down to the west. It was quite well defined. Above it in the east near the horizon was a red glow that showed up well in an image. What was really interesting was that as the arc strengthened in intensity curtains of light travelled along the arc from east to west. I was surprised at how quickly they were travelling. I would say that they covered about 15 degrees of arc in a few seconds.
This is only the second big display I have ever seen so my technical knowledge of how to describe it is poor. The arc dissipated about 18:45 and then returned again to the same strength. I took photos until about 19:10. A bit after that I could see some reddish glow due north (my dinner was ready so I had to go in!). Pictures to follow.
Hi David. I didn’t need to be logged in to read this pdf via this link, so I guess it is visible to non members too. Don’t know if this is an issue. Duncan.
Thanks Alex and David. I can see now it is obvious in the pdf version of the journal but it wasn’t very obvious in the printed version. Looking in better light I can now see it but it eluded me this morning. It seemed a bit like a “where’s Wally”. Tonally, it blended into the background or perhaps it is just me.
This star has now returned to its normal range of magnitudes. There is a paper that has appeared in the Astronomical Journal (https://iopscience.iop.org/article/10.3847/1538-3881/ace59d) where the authors have imaged the star during the great dimming using interferometry. They say that they saw an asymmetry in the stars photosphere which suggests a mass ejection of material. This would have cooled and formed a dust cloud that dimmed the star. This is similar to what happened to Betelgeuse in 2020.
Thanks very much for your detailed news item about the comet. I did try to find it Sunday morning but even though we have had some “clear skies” we have been plagued by hazy conditions and there was too much murk near the horizon to make it possible to view anything. I will try again, weather permitting, when it moves round to the evening sky in a few days time.
That’s a pretty amazing picture and a fantastic tail only marred by the curse of the satellite trail.
Thanks Nick. I did see this other forum post but I missed the detail about it remaining close to the sun. When I first read it I thought it was a discussion about visual comet finders versus automated surveys. I think it would be useful to have a specific news item that just describes what is going on with this comet in slightly more layman’s terms. Clearly some people are getting good pictures of it but it means getting up an hour before twilight?
I think it is annoying that this comet is getting heralded in the press as yet another comet for the general public to see but it sounds like it is anything but easy to follow.
I was very sorry to miss this meeting but I had a prior engagement that would have been difficult to break. I hope to join you all another time!
I was pleased to see that Z UMa has been highlighted in a recent facebook post. I have added the light curve of this variable star from this post below. As described, in the last year the maxima have become nicely double peaked and it has been suggested that this is due to the interaction of the two main periods of pulsation of this star. However, how does this square with the analysis of John Greaves that after 1995 there is little evidence for two pulsation periods in the data (see my earlier posts on this topic)?
I wondered if the timescales for the evolution of the double peak fit in with the two periods of 194.0 and 204.8 days that John measured before 1995. If you imagine that the two pulsation periods start out in phase, then after one period of each the peak of the 194.0 day pulsation will be ahead of the 204.8 day pulsation by 204.8 – 194.0 = 10.8 days. After n such periods, the shorter pulsation would be ahead by n x 10.8 days. Looking at the light curve for the star you can see that for the last double peak (September 2022 to November 2022) the two humps were separated by about 3 months or roughly 60 days. This would seem to imply that the two periods would have been in phase n = 60/10.8 ~ 6 periods earlier and this certainly seems feasible looking at the light curve.
So how often would we expect double peaks to be occurring if the two periods of 194.0 and 204.8 days persist? The simple linear addition of two sine curves of the same amplitude but different periods of A and B would result in another sine curve of period 2AB/(A+B) which in this case would be 199.3 days but the amplitude of this would be modulated by a cosine curve of 2AB/(A-B) which is 7,358 days or about 20 years. However, a cosine curve passes through zero twice every period, so the “beat” frequency is half this, i.e. every 10 years. This is only a very rough guide because I am sure that the behaviour is not linear but it seems reasonable given what I said in my earlier posts about how often double peaks occur. Interestingly, the amplitude of the light curve variations does decrease as a double hump approaches.
What is says to me is that we really need more accurate measurements of the light curve to better see what is going on. Have the two pulsation periods begun to die out as John says or are they being hidden in the noise of the data? Perhaps we need regular digital detector monitoring over the next 20 or 30 years to decide this. Anyone fancy this?
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It seems that the Universe may contain a lot of quantum entanglement. This must be a form of information and information bits have an energy cost. As energy equates to mass, I wonder if this contributes to the missing mass problem.
I am sorry I never got around to replying to your comment however I have just seen this article https://www.quantamagazine.org/physicists-use-quantum-mechanics-to-pull-energy-out-of-nothing-20230222/#comments and it makes interesting reading and may be relevant to what you say.
Duncan
On a slightly more serious note, and writing as a non-physicist, there seems to me something rather suspect about saying ‘Our model works – but only if we invent entities x and y.’ Might it not be an alternative to say, ‘The anomalies are so great that it looks as if our model doesn’t work. Perhaps it’s time to re-examine fundamental axioms and build a new model.’ Could we perhaps be heading for an exciting ‘paradigm-shift’?
Alan – agreed. The problem is that the standard model of cosmology works very well and it matches observations from very early times until now. It means that people are reluctant to accept a paradigm shift until there is overwhelming evidence to the contrary. It is like having a black box which predicts results for an experiment. If it keeps predicting the right results you might not be tempted to get your screwdriver out and fiddle with its innards in case you mess it up. Interestingly there are a few things on the horizon that may cause concern. One is the so called “Hubble Tension” (see for example https://www.scientificamerican.com/article/hubble-tension-headache-clashing-measurements-make-the-universes-expansion-a-lingering-mystery/) and the other would be if the James Webb Space Telescope starts seeing lots of well-formed galaxies at very high redshifts (see, for example, https://www.scientificamerican.com/article/jwsts-first-glimpses-of-early-galaxies-could-break-cosmology/)
Hi Adam. I have been messing about with some of the equations from that paper I mentioned above for the last few days. I thought, perhaps, that if the mass loss from the universe could be written into omega (matter) in equation (1) as something like omega (matter) = -kt + c for some time interval between, say, t1 and t2 (constant k>0 and c to be determined), then we could substitute this into equation (1) with omega (lamda) = 0 (i.e. no dark energy component but instead the matter density is decreasing constantly with time, that is the universe is losing mass). I found, though, that this doesn’t work and so it kind of blows my idea out of the water! The issue is that the second time derivative of the expansion factor d^2 a(t) / dt^2 < 0 which means that even though the universe continues to expand it does so at an ever decreasing rate. Of course, for the model with lamda the change in the rate of expansion goes from decreasing to zero to increasing.
I hope this makes sense.
A fascinating discussion – and I am looking forward to the conclusion as I try to lose weight every year around this time and would like some tips on how to do better in future!
Hi Alan. I would like to help you with your weight-loss plan, however, I think dark matter decay may not help you with your regime. I don’t think there is really enough of it in each of us to be helpful. This article https://www.universetoday.com/15266/dark-matter-is-denser-in-the-solar-system seems to imply that there might only be about 0.0018% mass of the earth in the whole solar system and I reckon, though I haven’t calculated what that equates to per meter cubed, that this doesn’t amount to much in each of us. Perhaps, a more effective way would to lose weight would be to cut your nails as did Tony in an episode of Men Behaving Badly that I recall.
Duncan.
PS Sorry about the edits – having trouble with my bbcodes!
For the so-called ‘benchmark universe’, matter and lambda, the scale factor, a(t), is proportional to (sinh(t))^(2/3).
Hi Adam. Thanks for taking this on and replying to my wacky ideas! To be honest I am trying to catch up with where you are with your understanding. I didn’t realize that in the matter dominated era in which we are now the scale factor a(t) for a lamda-CDM model could be so neatly expressed as a sinh(t) function. I found this paper (pdf) on the internet which I found helpful. I think their equation (5) is what you are referring to. What a beautifully elegant result! I always assumed that a model with lamda would be difficult to compute. So yes, as you say, this would be the benchmark to compare to. It has two nice asymptotic forms. When H0 t is << 1 the form is as in equation (6). The lamda term becomes negligible and a(t) is proportional to (t)^(2/3) which is like the Einstein-de Sitter model. When H0 t is >> 1 the form is as in equation (8) where the lamda term dominates and a(t) is proportional to exp(k t) where k is a constant which is like the de Sitter expansion model. I hope I have got this right!
I am going to split my replies due to issues of losing my posts when editing them.
Thanks for the suggestion Bill. I apologize that my use of the words “mass loss” is close to the term that is often used for stars. Stars, as you say, do lose mass all the time through nuclear burning but also through the stellar winds and evolutionary scenarios. Unfortunately, as Paul says, all that material and heat will just dissipate into another part of the universe and radiation and matter still contribute to the Universe’s gravity through Einstein’s general relativity theory. My idea of mass loss is a bit bonkers really. All of our notions of matter/energy are that this is a conserved quantity. You can’t just magic it away. However, in my defense I would say that we know very little about what the properties of dark matter are and so who is to say what it does. Also, in the past, theorists have had models where they consider the creation of matter as in the steady-state theory of Bondi, Gold and Hoyle (1948). So, if you can consider creating it, why not consider destroying it? Mine idea would be a big bang theory with reverse steady-state!
